The present invention relates to a luminescent device comprising a resonant microcavity having an active region.
In issued U.S. Pat. No. 5,469,018, which is incorporated herein by reference along with PCT Application PCT/US94/08306 (International Publication No. WO 95/03621), a resonant microcavity display and method of making same are disclosed. A resonant microcavity display is a luminescent display incorporating a thin-film phosphor embedded in a resonant microcavity. The microcavity resonator consists typically of an active region comprising a phosphor sandwiched between two reflectors or mirrors.
A display is further formed by coupling an excitation source to the microcavity. The phosphor inside the microcavity may be excited through several means including bombardment by externally generated electrons (cathodoluminescence), excitation by electrodes placed across the active layer to create an electric field (electroluminescence) or excitation using photons (photoluminescence).
The resonant microcavity display is typically characterized by a highly directional, monochromatic light distribution, oriented normal to the plane of the microcavity. As a result of the geometric design of the resonant microcavity, a resonant standing wave or traveling wave is produced which through constructive interference increases the emission of light in the forward direction, i.e., the direction perpendicular to the plane of the active layer. This light has the same frequency as the microcavity resonance and is thus monochromatic. The amount of light emitted in directions other than perpendicular to the active layer and at other frequencies other than the resonance is decreased because there is destructive interference in these directions and frequencies. The exact properties of the resonant microcavity display are calculated using quantum electrodynamics and solving Maxwell""s equations for the specific microcavity.
The subject invention is a resonant microcavity display utilizing mirrors which exhibit anomalous phase dispersion. It is the purpose of this invention to increase the amount of useable light generated by optimizing the internal net phase of the microcavity for all angles and wavelengths of potential emission. Anamolous phase dispersion can be defined as phase dispersion which is not an positive linear function of (cosine theta)/lambda, but rather decreasing, unchanging, or nonlinear over some useable range.
Altering the phase dispersion can increase or decrease the resonance mode volume in both wavelength and angle. This invention describes specific techniques to control both desired and undesired resonances.